1. Field of the Invention
The present invention relates to an imaging device and an endoscope apparatus including the same.
2. Description of the Related Art
A general endoscope apparatus generates an observation image by emitting white light from a white light source such as a xenon lamp, as illumination light, to an observation area in a body cavity through a light guide and capturing reflected light images due to the emission of the white light using an imaging element. The imaging element includes an electronic shutter, and adjusts the amount of received light by controlling an increase or decrease in the charge accumulation time using the electronic shutter. In the endoscope apparatus, light amount information is extracted from an image signal output from the imaging element, and the exposure time (shutter speed) by the electronic shutter is controlled based on the light amount information. For example, when the extracted light amount information is smaller than a reference value, the shutter speed is reduced to increase the amount of received light. In contrast, when the light amount information is larger than the reference value, the shutter speed is increased to reduce the amount of received light amount. As a result, since exposure according to the illumination light intensity and the observation target is performed, the brightness of the captured image can be maintained satisfactorily (refer to JP2005-270266A).
In recent years, instead of a white light source such as a xenon lamp, a semiconductor light source such as a laser light source or an LED light source has been adopted as a light source due to high efficiency and easy maintenance. Also for the imaging element, a complementary metal oxide semiconductor (CMOS) type image sensor having lower power consumption and higher reading speed than a charge coupled device (CCD) type imaging element has been adopted.